1. Field of the Invention
The present invention relates to a time keeping apparatus and a control method therefor, and more particularly to a radio-controlled timepiece having a power saving function to reduce its power consumption.
2. Description of the Related Art
A radio-controlled watch that has a power saving function and receives external time data (i.e. time signals received from outside the watch) and adjusts the time is disclosed in Japanese Patent Application Laid Open Publication No. 11-223684 entitled xe2x80x9cradio-controlled watchxe2x80x9d. The radio-controlled watch has a thermoelectric generator that generates electricity by using a temperature difference between the wearer""s arm and outside air. The watch stores the electricity in its storage unit and uses the electricity to operate.
The radio-controlled watch periodically receives a standard time radio signal from the Communications Research Laboratory (CRL) of Japan that is transmitted at a frequency of 40 kHz under a call sign of JJY (its former call sign was JG2AS). In the radio wave, time data is superimposed, and one set of the time data has a length of 60 seconds. The time data has data of the current hour, current minute, and current day that shows the number of days from January first of that year. Based on the time data, the time of the watch is adjusted.
However, the radio-controlled watch has a drawback. The drawback is that when a user wears the watch that was left unused (not worn on a user""s arm) for a long time, the user cannot know the correct time for several minutes. This is because the time adjustment of the watch is conducted only after the watch receives several sets of the time data. This is also because there are cases where the watch does not conduct a time adjustment, but continues to perform a time display: one such case is when the storage or storage unit voltage declines below a certain voltage where time display can become incorrect.
Accordingly, an object of the present invention is to provide a time keeping apparatus and a control method therefor, with which the user can know the current time more quickly and precisely when the operation mode of the apparatus is switched from the power saving mode to the normal operation mode.
According to one aspect of the present invention, a time keeping apparatus comprises: a generator unit that generates electricity using external energy; a storage unit that stores the electricity; a time display unit that displays time by using the electricity supplied from the storage unit; a generation state detecting unit that detects an operation state of the generator unit and that outputs a detected generation state signal; a mode switching unit that, responsive to the detected generation state signal, switches an operation mode between a normal operation mode in which the time display operation is performed, and a power saving mode in which the time display operation is stopped; a receiver unit that receives external time information in a prescribed cycle; a current time counting unit that renews current time information by referring to the time that corresponds to the time information received by the receiver unit; and a current time display switching unit that is responsive to the operation mode switching from the power saving mode to the normal operation mode to switch a state of the time display unit from a time display stoppage state to a current time display state in which a current time is displayed, based on the current time information; and wherein the mode switching unit switches the operation mode from the normal operation mode to the power saving mode when the state of the generator unit is detected in a non-generation state on the basis of the detected generation state signal.
According to another aspect of the present invention, a time keeping apparatus comprises: a generator unit that generates electricity using external energy; a storage unit that stores the electricity; a time display unit that performs a time display using the electricity supplied from the storage unit; a carry-state detecting unit that detects a carry-state of the time keeping apparatus and that outputs a detected carry-state signal; a mode switching unit that switches an operation mode of the time display unit between a normal operation mode in which the time display is performed and a power saving mode in which the time display is stopped, based on the detected carry-state signal; a receiver unit that receives external time information in a prescribed cycle; a current time counting unit that renews current time information by referring to the time that corresponds to the time information received by the receiver unit; and a current time display switching unit that is responsive to the operation mode switching from the power saving mode to the normal operation mode to switch a state of the time display unit from a time display stoppage state to a current time display state in which a current time is displayed, based on the current time information; and wherein the mode switching unit switches the operation mode from the normal operation mode to the power saving mode when the carry-state of the time keeping apparatus is detected to be in a non-carried state on the basis of the detected carry-state signal.
According to another aspect of the present invention, a method is provided for controlling a time keeping apparatus which comprises a generator unit that generates electricity by converting external energy to electrical energy and a time display unit that performs a time display, the method for controlling the time keeping apparatus comprising: detecting a state of generation of the generator unit and outputting a detected generation state signal; switching an operation mode of the time display unit between a normal operation mode in which the time display is performed and a power saving mode in which the time display is stopped, based on the detected generation state signal; receiving external time information in a predetermined cycle during the power saving mode; renewing current time information that corresponds to the current time by referring to the external time information received; and in response to the operation mode switching from the power saving mode to the normal operation mode, switching a state of the time display unit from a time display stoppage state to a current time display state in which a current time is displayed, based on the current time information; and wherein the operation mode switches from the normal operation mode to the power saving mode when the state of generation of the generator unit is detected to be in a non-generation state on the basis of the detected generation state signal.